The prostate gland surrounds the prostatic urethra, and enlargement of the prostate gland prevents passage of urine from the bladder. Enlargement of the prostate gland can result from the following etiologies: 1) benign prostatic hyperplasia (BPH); 2) carcinoma of the prostrate; 3) prostatitis; 4) post-procedural edema; 5) prostatic trauma; as well as others. Prostatic enlargement, is a common affliction among men. Prostatic enlargement is uncomfortable because it makes urination difficult or impossible. The condition is also dangerous because it can lead to infection of the bladder and kidneys, and severe cases may lead to death.
Lower urinary tract symptoms (LUTS), also common among older men, comprise a variety of conditions which can also lead to urinary retention and other complications resulting from retention. Some of the conditions falling under LUTS diagnosis include an enlarged prostate, BPH, and bladder outlet obstruction.
Prostatic enlargement can be treated with the implantation of a prostatic urethral stent. The stent serves to hold open the prostatic urethra to facilitate fluid flow during urination. A stent may be implanted, or delivered, as an interim solution to hold open the prostatic urethra while the patient awaits corrective treatment A stent may be implanted after thermal therapy or cryosurgery to keep the urethra open while post-treatment edema subsides. A stent may be implanted after radiation to keep the urethra open as the radiation effects on the prostatic tissue subside. Finally, a stent may be implanted as a primary treatment.
There are many different types of urethral stents. Generally, they are tubular in shape, and may be composed of solid tubes, coiled wire or ribbon, mesh, or braided filaments. Many stents are inserted, or delivered, into the urethra in a radially compressed form by a stent delivery system. After being properly positioned, these types of stents are radially expanded into their final shape, typically by thermal or mechanical means.
There are also non-expandable stents that are inserted into the urethra in their final form by a stent delivery system. These stents have an advantage over expandable stents in that the final configuration of the stent is known at the time of stent insertion.
During the first steps of the stent deployment process, the stent must be held in place on the stent delivery system during insertion. For expandable stents, this is typically accomplished by placing the stent inside a sheath, by crimping onto a catheter balloon, or by using a mechanical retainer or stopper.
Non-expandable stents are held in place on the stent delivery system by means of flexible tether strings (see U.S. Pat. No. 5,322,501 to Mahmud-Durrani) or a coiled wire fastening element (see U.S. Pat. No. 5,098,374 to Orthel-Jacobsen, et al.).
In the case of the Mahmud-Durrani delivery system, the stent is retained within the prostatic urethra by the same flexible tether strings, connected to a locating member. The locating member remains in the bladder as an anchoring means after the stent is delivered.
In the Orthel-Jacobsen delivery system, the coiled wire fastening element must be rotated by over 900 degrees in a screwing movement to release the stent from the fastening element.
Another consideration for urethral stent delivery is that it is usually better to deliver the stent to a location which allows uncompromised function of the bladder neck sphincter and the external sphincter. These sphincters control the flow of urine through the urethra. Obstruction of these sphincters leads to incontinence. To ensure the proper positioning of the stent, a number of prior art stent delivery systems provide position systems including visualization of the bladder and prostatic urethra during placement, mechanically locating off of the bladder neck, and anchoring of the stent delivery system in place during insertion.
In summary, prostatic enlargement is a common affliction among men. The symptoms of prostatic enlargement can be treated with the implantation of a urethral stent, which holds open the urethra to facilitate fluid flow during urination. Both expandable and non-expandable urethral stents have been used. The known final dimension of the non-expandable stents is a desirable feature. However, simple means for holding the non-expandable stent on the stent delivery system, and a simple method of deployment of non-expandable stents is desired.